The Last Gospel is the passage from the Gospel according to St. John in chapter i, verses 1 to 14 inclusive, where Jesus is described as the Logos. It is so named because it is part of the concluding rite of the Traditional Latin Mass of the Roman Rite.
The Last Gospel began as a private devotional practice on the priest's part, but was gradually absorbed into the rubrics of the Mass. Immediately, after the blessing, the priest goes to the Gospel side of the altar. He begins with the Dominus vobiscum as at the proclamation of the Gospel of the Mass. But, since he reads from the altar card, he makes a Sign of the Cross with his right thumb on the altar rather than on the Gospel text before signing his own forehead, lips, and chest. At the words Et Verbum caro factum est (And the Word became flesh), the priest genuflects.
The text of the Gospel is perhaps best known for its opening lines:
In principio erat Verbum, et Verbum erat apud Deum, et Deus erat Verbum... (In the beginning was the Word, and the Word was with God, and the Word was God...)
The third Mass of Christmas Day (where this same Gospel is read as the Gospel of the Mass) has no Last Gospel; before 1954, the Gospel for the Feast of the Epiphany would be used here. Also, a superseded Mass (e. g. if a feast of a Saint is superseded by a Sunday) could be commemorated by, among other things, having its Gospel as Last Gospel.